In U.S. Pat. No. 3,855,189, issued Dec. 17, 1974, there is described a polymerization process which comprises (a) introducing into a polymerization zone at least one polymerizable monomer selected from the group consisting of polymerizable conjugated dienes, polymerizable monovinyl-substituted aromatic compounds, and mixtures, under polymerization conditions employing an organolithium initiator, (b) polymerizing said polymerizable monomer with said organolithium initiator, thereby forming polymer-lithium moieties, (c) treating the resulting polymerization mixture with at least one polar compound in minor amount effective to improve coupling of said polymer-lithium, wherein said polar organic compound is ether, thioether, tertiary amine, or triazine or mixture, (d) treating said polymerization reaction system with at least one polyvinyl aromatic compound in minor amounts effective to couple said polymer-lithium moieties, wherein said polar compound is added to said polymerization mixture prior to or coincidentally with said polyvinyl aromatic compound. The amount of organolithium used is an amount to provide 0.02 to 2 equivalents of lithium per 100 parts by weight of monomer charged to the polymerization system, the effective amounts of polar compound ranges from 0.001 to 5 parts by weight per 100 parts of monomer in the system and the effective amount of polyvinyl aromatic coupling agent ranges from 0.005 to about 4 moles per gram equivalent of lithium used.
In U.S. Pat. No. 3,363,659, issued Jan. 16, 1968, there is disclosed a method of preparing polymers which consist essentially of butadiene and from 0.025 to about 0.4 parts by weight parts per hundred by weight of butadiene of a comonomer having at least two terminal .dbd.CH.sub.2 groups. These comonomers containing the .dbd.CH.sub.2 groups are said to be aliphatic, aromatic, cyclic, acyclic, or heterocyclic and the preferred compounds are benzenes and xylenes which are substituted by two or more vinyl groups. Thus, the preferred aromatics which modify comonomers are disclosed as being di-tri-tetra-penta-substituted benzene, including divinylbenzene. The polymerization catalyst therein disclosed was said to be alkyllithium compounds, such as butyllithium.
The present invention distinguishes from the prior art in that the U.S. Pat. No. 3,363,659 does not disclose the use of treating the active lithium terminated living polymers with polar compounds which form the basis of the present invention.
The present invention distinguishes from the U.S. Pat. No. 3,855,189 disclosure in that the present invention adds the polyvinyl aromatic compound prior to the polymerization of the conjugated diolefin monomer, not as a post-treatment as suggested in this reference.
The use of the polyvinyl aromatic compounds results in the formation of branched polymer chains.